1. Field of the Invention
The present invention relates to a radiation sensitive resin composition and, more particularly, to a radiation sensitive resin composition useful as a chemically amplified positive tone resist which is suitable for use in precision machining utilizing various types of radiation such as ultraviolet light, deep ultraviolet light, X-rays, or charged particle rays.
2. Description of the Background Art
Miniaturization of a design rule in lithography has been undergoing rapid progress in fields requiring fine work such as the manufacture of integrated circuit elements in order to achieve high integrity in ICs. Development of a lithography process capable of performing fine work, even of a size of 0.5 .mu.m or smaller, in a stable manner is actively being undertaken.
However, it is difficult to produce such a minute pattern at high precision by conventional methods using visible light (wavelength 700-400 nm) or near ultraviolet light (wavelength 400-300 nm). Because of this, lithography processes using radiation with a short wavelength (wavelength 300 nm or less), capable of achieving a wider depth of focus, and effective for miniaturizing a fine design rule has been proposed.
Examples of such lithography processes using short wavelength radiation are processes using a deep ultraviolet light such as a KrF excimer laser (wavelength 248 nm), an ArF excimer laser (wavelength 193 nm), X-rays such as synchrotron radiation, and charged particle rays such as an electron beam. A chemically amplified resist has been proposed by International Business Machines(IBM) as a high resolution resist used for such short wavelength radiation. Development and improvement of the chemically amplified resist are actively being undertaken at present.
A chemically amplified resist contains a radiation sensitive acid generator which generates an acid on being exposed to radiation. A chemical reaction, such as a change in polarity, cleavage of a chemical bond, or a cross-linking reaction is caused to occur in the resist coating by the catalytic action of the acid produced. This causes the solubility of the irradiated parts in a developing solution to change, thereby allowing a pattern to be produced in the resist coating.
Given as examples of conventional chemically amplified resists which exhibit relatively excellent resist performance are a resin containing an alkali-soluble resin in which the groups exhibiting affinity with an alkali are protected by a t-butyl ester group or t-butoxy carbonyl group (Japanese Patent Publication No. 27660/1990); a resin containing an alkali-soluble resin in which the groups exhibiting affinity with an alkali are protected by a silyl group (Japanese Patent Publication No. 44290/1991); a resin containing a (meth)acrylic acid component (Japanese Patent Publication No. 39665/1992), a resin containing an alkali-soluble resin in which the groups exhibiting affinity with an alkali are protected by a ketal group (Japanese Patent Application Laid-open No. 140666/1995); and a resin containing an alkali-soluble resin in which the groups exhibiting affinity with an alkali are protected by an acetal group (Japanese Patent Applications Laid-open No. 161436/1990 and No. 249682/1993).
However, it has been pointed out that all of these chemically amplified resists have peculiar problems which makes their commercial application difficult.
One serious problem is a situation where the line width of a resist pattern changes or the resist pattern is deformed into the form of a character "T" according to a post exposure delay (hereinafter abbreviated as "PED"), which is the period of time before the resist is baked (post baking) after irradiation.
In addition to these problems, there are problems such as fluctuation in resolution by PED, large dependency on the bake temperature, insufficient process stability, and the like. Further improvement in the overall characteristics of the chemically amplified resists is therefore strongly desired.
Among the above-described chemically amplified resists a positive tone resist containing a copolymer of hydroxystyrene and t-butyl acrylate as a resin component (hereinafter referred to as Type 1) and a positive tone resist containing a resin component with phenolic hydroxyl groups in poly(hydroxystyrene) protected with a ketal group or acetal group (hereinafter referred to as Type 2) are reported to have the above various problems only to a relatively small extent.
However, the Type 1 resist is easily affected by a standing wave because this resist contains a large amount of acrylic components having a small absorption coefficient at a wavelength of 248 nm, which gives rise to an impaired pattern configuration. The Type 1 resist also exhibits only poor resolution. The Type 2 resist, on the other hand, exhibits only poor heat resistance, giving rise to pattern deformation due to heat. In the situation where demand for miniaturization increases, these resists cannot satisfy all requirements, such as high resolution, excellent heat resistance, and the like, at the same time.
In view of this situation, the present invention has been completed as a result of detailed studies relating to resin components comprising chemically amplified resists. Specifically, an object of the present invention is to provide a radiation sensitive resin composition useful as a chemically amplified positive tone resist, which is sensitive to various types of radiation and which exhibits high resolution, superb capability of producing superior pattern forms, and excellent resistance to PED, higher process stability, is affected by a standing wave only to a minimum extent, and possesses prominent heat resistance.